CN116224244A

CN116224244A - Generation method of Rang-Doppler graph and related device

Info

Publication number: CN116224244A
Application number: CN202211711657.XA
Authority: CN
Inventors: 贾新迪; 张景宇; 靳辉凯; 陈盼; 芦俊伟; 付乐乐; 孙世川; 王晓蕾; 吴英强; 秦屹
Original assignee: Whst Co Ltd
Current assignee: Whst Co Ltd
Priority date: 2022-12-29
Filing date: 2022-12-29
Publication date: 2023-06-06

Abstract

The application provides a method and a related device for generating a Rang-Doppler graph. The method comprises the following steps: respectively acquiring Rang-Doppler graphs corresponding to R paths of target echo data of the radar, and forming digital beams to obtain Rang-Doppler graphs corresponding to M beams; constant false alarm detection is carried out on the Rang-Doppler graphs corresponding to the M wave beams; for each index position in the Rang-Doppler graph, if the RD data corresponding to the index position comprises a cfar point, taking the maximum value in M RD data of the index position as the RD data of the index position in the final Rang-Doppler graph; and if the RD data corresponding to the index position does not comprise the cfar point, determining the RD data of the index position based on the M RD data corresponding to the index position. The method and the device can reduce the transmission time length and simultaneously reduce the loss of signal to noise ratio.

Description

Generation method of Rang-Doppler graph and related device

Technical Field

The application relates to the technical field of radars, in particular to a method for generating a Rang-Doppler graph and a related device.

Background

Millimeter wave radar has the advantages of complex environment imaging, long-distance tracking, high resolution and the like, and becomes one of the most effective tools in the remote sensing field. In the using process of the radar product, besides directly outputting target information, cfar information, RD (Range-Doppler) diagrams and the like are also derived as debugging means, and detection is performed again. However, due to limitations of storage space, update rate, network rate, etc., the radar PS (Processing System ) end cannot receive all information from the PL (Progarmmable Logic, programmable logic) end, which results in a certain loss of information output from the radar, which is particularly prominent in the transmission process of the RD diagram.

In the prior art, in order to enhance the signal power in a specific direction and improve the anti-interference performance of a radar system, a Digital Beam Forming (DBF) method is mostly adopted in the radar, however, in the scheme of outputting an RD diagram, the following disadvantages exist in the method:

1. all the multiple RD graphs obtained by digital beam forming at the radar PL end are transmitted to the PS end, but the transmission time length must be increased due to the limitation of the network rate, so that the radar update period is longer, and the target dynamics cannot be displayed in real time.

2. Under the condition of ensuring the radar update rate, the PL end performs digital beam forming, but outputs a non-coherent accumulation RD graph, so that the target signal-to-noise ratio is lost, and the detection rate of a large-angle target and a long-distance target is lower.

Disclosure of Invention

The application provides a method and a related device for generating a Rang-Doppler graph, which are used for solving the problem of reduced target signal-to-noise ratio on the premise of guaranteeing radar update rate.

In a first aspect, the present application provides a method for generating a rag-Doppler plot, where the method is applied to a programmable logic device of a radar, and includes:

respectively acquiring Rang-Doppler graphs corresponding to R paths of target echo data of the radar; the Rang-Doppler plot includes RD data; r is more than or equal to 1;

carrying out digital beam forming on the Rang-Doppler graphs corresponding to the R paths of receiving channels to obtain Rang-Doppler graphs corresponding to M beams; m is more than or equal to 1;

performing constant false alarm detection on the Rang-Doppler graphs corresponding to the M wave beams to obtain cfar points in the Rang-Doppler graphs;

for each index position in the M Rang-Doppler graphs, if the M RD data corresponding to the index position comprises a cfar point, taking the maximum value in the M RD data corresponding to the index position as the RD data of the index position in the final Rang-Doppler graph; and if the RD data corresponding to the index position does not comprise cfar points, determining the RD data of the index position in the final Rang-Doppler graph based on the M RD data corresponding to the index position.

In a second aspect, the present application provides an apparatus for generating a rag-Doppler plot, the apparatus being applied to a programmable logic device of a radar, the apparatus comprising:

the Rang-Doppler graph generation module is used for respectively acquiring Rang-Doppler graphs corresponding to R paths of target echo data of the radar; the Rang-Doppler plot includes RD data; r is more than or equal to 1;

the beam forming module is used for carrying out digital beam forming on the Rang-Doppler graphs corresponding to the R paths of receiving channels to obtain Rang-Doppler graphs corresponding to the M beams; m is more than or equal to 1;

the constant false alarm detection module is used for performing constant false alarm detection on the Rang-Doppler graphs corresponding to the M wave beams to obtain cfar points in the Rang-Doppler graphs;

the generating module of the final Rang-Doppler graph is used for aiming at each index position in the M Rang-Doppler graphs, if the M RD data corresponding to the index position comprises a cfar point, taking the maximum value in the M RD data corresponding to the index position as the RD data of the index position in the final Rang-Doppler graph; and if the RD data corresponding to the index position does not comprise cfar points, determining the RD data of the index position in the final Rang-Doppler graph based on the M RD data corresponding to the index position.

In a third aspect, the present application provides a radar comprising a memory, a processor and a computer program stored in the memory and executable on the processor, the processor implementing the steps of the method according to any one of the possible implementations of the first aspect above when the computer program is executed.

In a fourth aspect, embodiments of the present application provide a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the method as described in any one of the possible implementations of the first aspect above.

The embodiment of the application provides a generation method of a Rang-Doppler graph and a related device, wherein the method comprises the steps of firstly, respectively obtaining the Rang-Doppler graph corresponding to R paths of target echo data of a radar; the Rang-Doppler plot includes RD data; then, carrying out digital beam forming on the Rang-Doppler graphs corresponding to the R paths of receiving channels to obtain Rang-Doppler graphs corresponding to M beams; performing constant false alarm detection on the Rang-Doppler graphs corresponding to the M wave beams to obtain cfar points in the Rang-Doppler graphs; finally, aiming at each index position in the M Rang-Doppler graphs, if the M RD data corresponding to the index position comprises cfar points, taking the maximum value in the M RD data corresponding to the index position as the RD data of the index position in the final Rang-Doppler graph; and if the RD data corresponding to the index position does not comprise cfar points, determining the RD data of the index position in the final Rang-Doppler graph based on the M RD data corresponding to the index position. The method and the device can output a final Rang-Doppler graph of beam forming, so that transmission time is reduced, radar update rate is guaranteed, and meanwhile, the final Rang-Doppler graph can contain cfar points detected by digital beam forming to the greatest extent, and accordingly loss of signal to noise ratio is reduced.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required for the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flowchart of an implementation of a method for generating a Rang-Doppler graph provided in an embodiment of the present application;

FIG. 2 is a schematic structural diagram of a generating device of a Rang-Doppler graph according to an embodiment of the present application;

fig. 3 is a schematic diagram of a radar provided in an embodiment of the present application.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system configurations, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

For the purpose of making the objects, technical solutions and advantages of the present application more apparent, the following description will be made with reference to the accompanying drawings by way of specific embodiments.

Referring to fig. 1, a flowchart of an implementation of a method for generating a rag-Doppler graph according to an embodiment of the present application is shown, and details are as follows:

s101: respectively acquiring Rang-Doppler graphs corresponding to R paths of target echo data of the radar; the Rang-Doppler plot includes RD data; r is more than or equal to 1.

Specifically, the method is applied to a programmable logic device of a radar, and the radar provided by the embodiment adopts a transmitting channel to transmit a frequency modulation continuous wave signal in a frame unit, the signal bandwidth is B, and the frequency modulation is performedWith width T, a frame contains N _d And frequency modulated signals. The radar receives the frequency modulation signals returned after the transmitted signals meet the target through R receiving channels, mixes, filters and ADC samples the target echo signals to obtain target echo data, wherein the sampling rate is f _s The number of sampling points in one frequency modulation signal is N _r ＝T·f _s . Thus, the target echo data received by each receive channel may be arranged into an N _d ×N _r The matrix of echo data corresponding to each receiving channel is respectively marked as S ₁ ,S ₂ ……S _R 。

In one possible implementation, the specific implementation procedure of S101 includes:

and (3) performing Doppler and distance-dimension FFT (Fast Fourier Transformation) processing on the R-path target echo data respectively to obtain R Rang-Doppler graphs corresponding to the R-path receiving channels one by one.

In one possible embodiment, the target echo data is N _d Row N _r An echo data matrix of columns; wherein N is _d Representing the number of frequency modulation signals included in one path of target echo data, N _r Representing the number of sampling points included in a frequency modulated signal; the specific implementation flow of S101 further includes:

for each path of target echo data, N is carried out on each line in the path of echo data matrix _1DFFT FFT calculation of points to obtain a one-dimensional FFT data matrix; n for each column in the one-dimensional FFT data matrix _2DFFT And (3) carrying out FFT (fast Fourier transform) calculation on the points to obtain a Rang-Doppler diagram corresponding to the echo data matrix.

Specifically, for each path of target echo data, N is made for each line of target echo data in the echo data matrix _1DFFT FFT calculation of the points to obtain a one-dimensional FFT data matrix S _1FFT1 ,S _1FFT2 ……S _1FFTR Then respectively for one-dimensional FFT data matrix S _1FFT1 ,S _1FFT2 ……S _1FFTR N is made for each column of data in the data _2DFFT FFT calculation of points to obtain a two-dimensional FFT data matrix S _2FFT1 ,S _2FFT2 ……S _2FFTR Each two-dimensional post-FFT data matrix is a rag-Doppler plot.

In this embodiment, the range-Doppler graph includes RD (range-Doppler) data, where the RD data is two-dimensional data including range information (range) and velocity information (Doppler), where the range information is a distance between radar targets and the radar, and the velocity information is a radial velocity between the radar targets.

S102: carrying out digital beam forming on the Rang-Doppler graphs corresponding to the R paths of receiving channels to obtain Rang-Doppler graphs corresponding to M beams; m is more than or equal to 1.

In one possible implementation, the specific implementation procedure of S102 includes:

acquiring Rang-Doppler graphs corresponding to M beams based on a first formula, wherein the first formula is as follows:

wherein W is _MR Representing a weight coefficient corresponding to an R-th receiving channel of an M-th wave beam; s is S _2FFTR Representing a Rang-Doppler plot corresponding to the R-th receive channel, C _M And shows a Rang-Doppler diagram corresponding to the Mth beam.

In particular, the method comprises the steps of,

represents a weighting matrix, thus W _M Representing the weight coefficient corresponding to the R-th receiving channel of the M-th beam, C _M Is N _1DFFT ×N _2DFFT Is a matrix of (a); since the Rang-Doppler plot is a two-dimensional complex matrix, the weight coefficients are complex.

S103: and performing constant false alarm detection on the Rang-Doppler graphs corresponding to the M beams to obtain cfar (Constant False Alarm Rate Detector, detector under constant false alarm probability) points in the Rang-Doppler graphs.

In this embodiment, amp is used as a target amplitude, constant false alarm detection is performed on a Rang-Doppler graph corresponding to M beams, and RD data with amplitude greater than Amp in the Rang-Doppler graph is used as a cfar point.

S104: for each index position in the M Rang-Doppler graphs, if the M RD data corresponding to the index position comprises a cfar point, taking the maximum value in the M RD data corresponding to the index position as the RD data of the index position in the final Rang-Doppler graph; and if the RD data corresponding to the index position does not comprise cfar points, determining the RD data of the index position in the final Rang-Doppler graph based on the M RD data corresponding to the index position.

Specifically, each Rang-Doppler plot is N _1DFFT Row, N _2DFFT And (3) the array of columns, wherein the index position comprises an index row and an index column, and for the same index position in the M Rang-Doppler graphs, if the plurality of RD data corresponding to the index position comprises RD data with amplitude larger than Amp, namely cfar points, the RD data corresponding to the maximum amplitude value in the plurality of RD data corresponding to the index position is taken as the RD data of the index position in the final Rang-Doppler graph.

And if the plurality of RD data corresponding to the index position does not comprise RD data with the amplitude larger than Amp, acquiring the median of the plurality of RD data corresponding to the index position as the RD data of the index position in the final Rang-Doppler graph.

Thus, after the RD data of each index position is determined according to the method, a final Rang-Doppler graph can be obtained, and cfar points can be reserved in the final Rang-Doppler graph as much as possible, so that the loss of the target signal-to-noise ratio is avoided.

In one possible implementation, determining the RD data for the index position in the final rag-Doppler plot based on the M RD data corresponding to the index position in S104 includes:

and taking the average value of M RD data corresponding to the index position as the RD data of the index position in the final Rang-Doppler graph.

In one possible implementation manner, the method provided by the embodiment further includes:

and sending the final Rang-Doppler graph to a processing system side of the radar.

Specifically, the processing system side makes subsequent decisions based on the final Rang-Doppler graph, and can improve target detection accuracy based on the final Rang-Doppler graph with high signal-to-noise ratio.

As can be seen from the above embodiments, the method provided in this embodiment firstly performs digital beam forming to obtain multiple RD graphs, and after a certain method selection, only outputs one RD graph finally, so as to save storage resources, reduce the requirement for network rate, and is not limited by the network transmission rate, thereby improving the target update rate; and the present embodiment may include the cfar points detected by digital beamforming to the maximum extent compared to a RD plot formed by non-coherent accumulation, with substantially no loss in signal-to-noise ratio.

It should be understood that the sequence number of each step in the foregoing embodiment does not mean that the execution sequence of each process should be determined by the function and the internal logic of each process, and should not limit the implementation process of the embodiment of the present application in any way.

The following are device embodiments of the present application, for details not described in detail therein, reference may be made to the corresponding method embodiments described above.

Fig. 2 shows a schematic structural diagram of a device for generating a rag-Doppler plot according to an embodiment of the present application, where the device is applied to a programmable logic device of a radar, and for convenience of explanation, only a portion relevant to the embodiment of the present application is shown, and details are as follows:

as shown in fig. 2, the device 100 for generating a rag-Doppler plot includes:

the Rang-Doppler graph generation module 110 is configured to respectively obtain Rang-Doppler graphs corresponding to R paths of target echo data of the radar; the Rang-Doppler plot includes RD data; r is more than or equal to 1;

the beam forming module 120 is configured to perform digital beam forming on the rag-Doppler graphs corresponding to the R paths of receiving channels, so as to obtain rag-Doppler graphs corresponding to the M beams; m is more than or equal to 1;

the constant false alarm detection module 130 is configured to perform constant false alarm detection on the Rang-Doppler graphs corresponding to the M beams, so as to obtain cfar points in the Rang-Doppler graphs;

the final rag-Doppler graph generating module 140 is configured to, for each index position in the M rag-Doppler graphs, if the M RD data corresponding to the index position includes a cfar point, take the maximum value in the M RD data corresponding to the index position as the RD data of the index position in the final rag-Doppler graph; and if the RD data corresponding to the index position does not comprise cfar points, determining the RD data of the index position in the final Rang-Doppler graph based on the M RD data corresponding to the index position.

In one possible implementation, the Rang-Doppler graph generation module 110 includes:

and carrying out FFT processing on the R paths of target echo data in Doppler and distance dimensions respectively to obtain R Rang-Doppler graphs corresponding to the R paths of receiving channels one by one.

In one possible embodiment, the target echo data is N _d Row N _r An echo data matrix of columns; wherein N is _d The method comprises the steps that the number of frequency modulation signals included in one path of target echo data is represented, and Nr represents the number of sampling points included in one frequency modulation signal; the Rang-Doppler plot generation module 110 further includes:

In one possible implementation, the beam forming module 120 includes:

In one possible implementation, the final Rang-Doppler plot generation module 140 includes:

In one possible implementation manner, the generating device of the Rang-Doppler graph further comprises:

and the communication module is used for sending the final Rang-Doppler graph to the processing system side of the radar.

As can be seen from the above embodiments, the device provided in this embodiment firstly performs digital beam forming to obtain multiple RD graphs, and selects a certain method to output only one RD graph finally, so as to save storage resources, reduce the requirement of network rate, and is not limited by the network transmission rate, thereby improving the target update rate; and the present embodiment may include the cfar points detected by digital beamforming to the maximum extent compared to a RD plot formed by non-coherent accumulation, with substantially no loss in signal-to-noise ratio.

Fig. 3 is a schematic diagram of a radar provided in an embodiment of the present application. As shown in fig. 3, the radar 3 of this embodiment includes: a processor 30, a memory 31 and a computer program 32 stored in said memory 31 and executable on said processor 30. The steps in the above-described embodiments of the method for generating a Rang-Doppler plot are implemented by the processor 30 when executing the computer program 32, for example, steps S101 to S104 shown in fig. 2. Alternatively, the processor 30 may perform the functions of the modules/units of the apparatus embodiments described above, such as the functions of the modules 110-140 of fig. 2, when executing the computer program 32.

Illustratively, the computer program 32 may be partitioned into one or more modules/units that are stored in the memory 31 and executed by the processor 30 to complete/implement the schemes provided herein. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions describing the execution of the computer program 32 in the radar 3. For example, the computer program 32 may be partitioned into modules 110 through 140 shown in FIG. 2.

The radar 3 may include, but is not limited to, a processor 30, a memory 31. It will be appreciated by those skilled in the art that fig. 3 is merely an example of radar 3 and is not meant to be limiting of radar 3, and may include more or fewer components than shown, or may combine certain components, or different components, e.g., the radar may also include input-output devices, network access devices, buses, etc.

The processor 30 may be a central processing unit (Central Processing Unit, CPU), other general purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), field-programmable gate arrays (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

The memory 31 may be an internal storage unit of the radar 3, such as a hard disk or a memory of the radar 3. The memory 31 may be an external storage device of the radar 3, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card) or the like, which are provided on the radar 3. Further, the memory 31 may also include both an internal memory unit and an external memory device of the radar 3. The memory 31 is used for storing the computer program as well as other programs and data required by the radar. The memory 31 may also be used for temporarily storing data that has been output or is to be output.

It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-described division of the functional units and modules is illustrated, and in practical application, the above-described functional distribution may be performed by different functional units and modules according to needs, i.e. the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-described functions. The functional units and modules in the embodiment may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit, where the integrated units may be implemented in a form of hardware or a form of a software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working process of the units and modules in the above system may refer to the corresponding process in the foregoing method embodiment, which is not described herein again.

In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

In the embodiments provided in this application, it should be understood that the disclosed apparatus/radar and method may be implemented in other ways. For example, the apparatus/radar embodiments described above are merely illustrative, e.g., the division of the modules or elements is merely a logical functional division, and there may be additional divisions in actual implementation, e.g., multiple elements or components may be combined or integrated into another system, or some features may be omitted, or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection via interfaces, devices or units, which may be in electrical, mechanical or other forms.

The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present application may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.

The integrated modules/units, if implemented in the form of software functional units and sold or used as stand-alone products, may be stored in a computer readable storage medium. Based on such understanding, the present application may implement all or part of the flow of the method of the foregoing embodiment, or may be implemented by implementing a computer program to instruct related hardware, where the computer program may be stored in a computer readable storage medium, where the computer program, when executed by a processor, may implement the steps of the generating method embodiments of the various rag-Doppler graphs. Wherein the computer program comprises computer program code which may be in source code form, object code form, executable file or some intermediate form etc. The computer readable medium may include: any entity or device capable of carrying the computer program code, a recording medium, a U disk, a removable hard disk, a magnetic disk, an optical disk, a computer Memory, a Read-Only Memory (ROM), a random access Memory (Random Access Memory, RAM), an electrical carrier signal, a telecommunications signal, a software distribution medium, and so forth. It should be noted that the computer readable medium may include content that is subject to appropriate increases and decreases as required by jurisdictions in which such content is subject to legislation and patent practice, such as in certain jurisdictions in which such content is not included as electrical carrier signals and telecommunication signals.

Furthermore, the features of the embodiments shown in the drawings or mentioned in the description of the present application are not necessarily to be construed as separate embodiments from each other. Rather, each feature described in one example of one embodiment may be combined with one or more other desired features from other embodiments, resulting in other embodiments not described in text or with reference to the drawings.

The above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.

Claims

1. The method for generating the Rang-Doppler graph is characterized by being applied to a programmable logic device of a radar and comprising the following steps of:

2. The method for generating a Rang-Doppler plot according to claim 1, wherein the steps of respectively acquiring a Rang-Doppler plot corresponding to R-path target echo data of a radar include:

3. The method for generating a rag-Doppler plot according to claim 2, wherein the target echo data is N _d Row N _r An echo data matrix of columns; wherein N is _d The method comprises the steps that the number of frequency modulation signals included in one path of target echo data is represented, and Nr represents the number of sampling points included in one frequency modulation signal;

the Doppler and distance dimension FFT processing is respectively carried out on the R paths of target echo data to obtain R Rang-Doppler graphs corresponding to the R paths of receiving channels one by one, and the method comprises the following steps:

4. The method for generating a rag-Doppler plot according to claim 1, wherein the performing digital beam forming on the rag-Doppler plot corresponding to the R-path receiving channel to obtain a rag-Doppler plot corresponding to M beams includes:

5. The method for generating a rag-Doppler plot according to claim 1, wherein determining the RD data of the index position in the final rag-Doppler plot based on the M RD data corresponding to the index position comprises:

6. The method for generating a rag-Doppler plot according to claim 1, further comprising:

7. A device for generating a rag-Doppler plot, the device being applied to programmable logic of a radar, the device comprising:

8. The device for generating a rag-Doppler plot according to claim 7, wherein the rag-Doppler plot generating module comprises:

9. Radar comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor implements the steps of the method of generating a rag-Doppler plot according to any of the preceding claims 1 to 6 when the computer program is executed by the processor.

10. A computer readable storage medium storing a computer program, characterized in that the computer program when executed by a processor implements the steps of the method of generating a rag-Doppler plot according to any one of the preceding claims 1 to 6.